When members of St. Philip’s Episcopalian Church gathered on their grounds in Annapolis for a stewardship project last spring, it rained.

A few months later, a television crew came to film the project. It rained again.

But their project was a rain garden, so the wet weather proved a fitting backdrop to the cause at hand.

“We put in the rain garden because it was a great way to catch some of the runoff from our parking lot,” said the Rev. Angela Shepherd. “The rain showed us right away what the whole process would lead to. The water was pouring right into the area as we worked, and making this little pool.”

Rain gardens are an increasingly popular way to combat the ill effects of stormwater runoff and the pollution it washes into streams, rivers, and the Chesapeake Bay. Rain gardens have been created on all kinds of properties, including those of businesses and private homes.

At a glance, rain gardens look like normal garden beds featuring native plants—with butterflies hovering by clusters of pink Joe Pye Weed, or a goldfinch perched on the knobby center of a coneflower.

Rain gardens are attractive, inviting places, where people like to linger. They serve as a backdrop for home patios or outdoor lunches at business sites. At St. Philip’s, benches surround the garden where parishioners can visit for prayer and meditation. On Earth Day 2007, they will dedicate a stone altar and begin using the site for worship.

But rain gardens also have a job to do.

Resting in a shallow depression—usually about 6 inches deep—a rain garden is designed to collect stormwater and allow it to evaporate or seep into the ground within a day or two.

Some of the pooling water helps the plants to grow, and some of it soaks deep into the earth to replenish ground water. The process also filters nitrogen, phosphorus and other contaminants that enter the water from rooftops and driveways.

Absorbing rainwater where it falls has become increasingly important in the Bay watershed, where the growing number of rooftops and amount of pavement can compound stormwater runoff into a torrential flow.

“Stormwater has become one of the biggest threats to our waterways,” said Tiffany Wright, a watershed analyst at the Center for Watershed Protection. “When we minimize runoff and the pollutants associated with it, we protect water quality.”

According to the center, a single house with a 1,000 square-foot roof yields 600 gallons of water from a 1-inch rainstorm.

The strength and volume of runoff from a variety of hard surfaces combine to erode stream banks and flood roads. It also washes untreated pollutants directly into local streams and rivers.

Runoff from urban areas delivers about 16 percent of phosphorus, 11 percent of nitrogen and 9 percent of sediment loads to the Chesapeake, according to Bay Program estimates, and severely impact more than 1,570 miles of streams in the watershed.

The congregation at St. Philip’s learned about rain gardens through the outreach efforts of Anne Pearson, director of the Alliance for Sustainable Communities. At the time, they were planning to expand their parking lot. Pearson introduced them to rain gardens as a way to minimize their impact on local waters.

“I’ve always been aware of environmental issues and, as a church, we look for avenues to make a statement to the broader world,” Shepherd said. “The rain garden was an opportunity for us to do this.”

They worked with Pearson to plan the rain garden and secured grants for the project from the Chesapeake Bay Trust and Unity Gardens.

“We had walked the grounds and picked out a site we thought would be perfect for the rain garden,” Shepherd said. “But later, when Ann, a landscape engineer, and I were looking at the space in the rain, we discovered the ideal location.”

In its simplest form, a rain garden is a depressed bed where the soil has been dug approximately 2 feet deep and is enriched with organic matter and, sometimes, sand. The rain garden may be located in a flat area or on a gentle slope, but the plant bed itself is designed to promote pooling.

Downspouts or berms direct runoff into the garden, which is filled with native plants. Native species are best suited to the range of dry and wet conditions that the rain garden will experience.

A typical home rain garden ranges from 100 to 300 square feet and often captures the runoff from one downspout, or about one-fourth of the rooftop area. Smaller rain gardens have less plant variety, but can still control a high percentage of stormwater.

Larger gardens take longer to dig, level and plant, but may be needed to accommodate larger drainage areas, like those on commercial sites. Some large drainage rain gardens include an underdrain—an underground pipe that moves water further into the ground or to a more traditional drainage system.

At St. Philip’s, the rain garden is located on land sloping away from the base of their parking area. No drain was needed because the sandy soil was excellent for natural drainage.

“Our garden is an oval shape, about 15 to 20 feet wide and about 30 to 40 feet long,” Shepherd said. “We planted it on Earth Day. The rain was quite heavy, but it was fun.”

When the wet weather created an immediate pool of water in the rain garden, some parishioners approached Pearson with questions.

“They said, ‘Ann, I didn’t think we were making a pond,’ ” Pearson said. “I asked them to wait and see what happened. They’ve been thrilled.”

Along with benches, clay tiles have been added to enhance the garden, with text and images that relate to earth and water. Artful signs describe the interconnectedness of God, humans, earth and water. The text closes with a call to action: “We can each make rain gardens at home to do our part in restoring the rivers that are our heritage.”

A rain garden costs little if one prepares the bed oneself and uses plants donated by neighbors or transplanted from other places in one’s yard. When buying plants, the cost averages $3 to $5 per square foot. Hiring a landscaper to handle the job, might cost $10 to $12 per square foot.

Like any new planting, the rain garden may need watering for the first few weeks. Some weeding, thinning and replacement plants will also be needed over time.

“But except for major droughts, you don’t have to worry about watering your garden. It will survive without you,” Pearson said.